Late 17th century (in an earlier sense). From classical Latin octōgēnārius containing eighty, aged eighty, in post-classical Latin also used as noun denoting a person aged eighty from octōgēnī eighty each (from octōgintā eighty (from octo eight + -gintā, suffix forming cardinal numerals from thirty to ninety, related to decem ten: see decem-) + -ēnī, suffix forming distributive adjectives, after e.g. sēnī six apiece, six at a time, six) + -ārius. Compare Middle French, French octogénaire,, Italian ottogenario, †octuagenario, Spanish octogenario.